1. The Field of the Invention
The present invention relates generally to the manner of connecting a flexible circuit to adjacent electrical devices. More particularly, the present invention relates to the configuration of flexible circuits that connect electrical devices to a printed circuit board.
2. The Relevant Technology
Transceiver modules are widely used in the field of optoelectronics. Typically, a transceiver module includes a transmitter optical subassembly (TOSA) and a receiver optical subassembly (ROSA). Each of the TOSA and the ROSA may have an optical receptacle, for example a Lucent Connector (LC) cable receptacle or a Standard Connector (SC) cable receptacle, at one end, for attachment to an optical cable. They may also have a connector to provide an electrical connection to a printed circuit board at the other end. The entire transceiver module, in turn, connects to a computer system, such as a host system, for controlling the operation of the transceiver module. Thus, the computer system can direct the transceiver module to transmit an optical signal by directing an electronic signal through the printed circuit board and into the TOSA. The TOSA then generates an optical signal via an internal laser or light emitting diode (LED) and directs the optical signal into the outgoing optical cable. Similarly, the ROSA receives an optical signal via a photodiode from the incoming optical cable and transmits the signal to a printed circuit board and on to the computer system.
Providing an optimal connection between a TOSA and/or a ROSA and a printed circuit board, however, can be difficult. For example, positioning of the TOSA and the ROSA within the transceiver module must occur to small tolerances to achieve the desired optical performance. Similarly, precise alignment of the printed circuit board (PCB) relative to the TOSA and/or the ROSA must occur. Rigidly connecting the PCB to the TOSA and/or ROSA increases the difficulty with accurately positioning the devices difficult. Additionally, including the rigid connection can cause damage to the PCB, TOSA, and/or ROSA when the module experiences vibration and movement as optical cables are moved, attached and detached. Additionally, differential thermal contraction/expansion can also cause problems if the PCB rigidly connects to the TOSA and/or the ROSA.
To limit these problems, flexible circuits may be disposed between the TOSA and/or ROSA and the printed circuit board to electrically interconnect them while isolating the PCB from vibration or thermal expansion or contraction of the adjacent devices. The flexible circuit is additionally advantageous in that, during production, the PCB may be mechanically fixed in place while the TOSA and/or ROSA are not, or vice versa. Accordingly, a flexible circuit is frequently used to assemble the module so that variations in device subassembly position do not prevent precise connections and alignments from being made between the TOSA and/or ROSA and the printed circuit board.
Flexible circuits typically include a number of conductors or traces of conductive material that are bonded to or applied to a thin, flexible dielectric. Flexible circuits have a number of advantages when compared with other manners of connecting electrical components, such as the PCB to the TOSA and/or the ROSA. For instance, flexible circuits provide greater reliability than wire connections and eliminate the need for mechanical connectors, while reducing the possibility of wiring mistakes. Additionally, flexible circuits are typically lighter, require less space, provide higher circuit density, and are lower cost than other types of wire connections.
Although flexible circuits are beneficial, one of the difficulties associated with flexible circuit design is determining where to place the traces and components on the circuit. For instance, as optical devices such as TOSAs increase in performance and speed, additional conductive traces with different shapes and connectivity requirements are required. The number of such traces, as many as fifteen or more often exceeds the capacity for conventional flexible circuit designs to make contact with adjacent electronic devices. Additionally, both because devices are manufactured according to industry standards and due to the industry pressure for increasingly smaller devices, simply enlarging the size of a contact interface is not always an option.
Due to desired characteristics of flexible circuits, i.e., the flexible circuit is bendable, manufacturing processes require the inclusion of tooling holes to allow the flexible material to be fixed in place while the various components and traces are mounted on the circuit. Traditionally, these tooling holes are drilled somewhere in the middle of the flexible circuit. Unfortunately, this placement of a tooling hole eliminates space that could be used for the circuits or traces. As components become smaller and smaller, this space can be needed for additional circuitry as described above.
Accordingly, what is needed are novel devices and systems for improving the manufacturability of a flexible circuit while simultaneously providing the opportunity to increase circuit density of the flexible circuit.